Methanol production process

ABSTRACT

A process for the production of methanol comprises feeding an amount of a hydrocarbon feedstock and an amount of an oxygen feedstock to a partial oxidation reactor to produce a partial oxidation reactor effluent comprising hydrogen, carbon monoxide and carbon dioxide; adding an amount of a hydrogen feedstock to the partial oxidation reactor effluent to produce a synthesis gas stream having a predetermined ratio of hydrogen to carbon monoxide; and, subjecting the synthesis gas stream to methanol synthesis to produce a methanol product stream and a tail gas stream wherein reformation is not used to provide hydrogen as a product. Reformation may be used to consume hydrogen so that carbon dioxide preferably obtained as a by product of another process so that the instant process becomes effectively a temporary carbon sink to convert carbon dioxide, which would otherwise be released to the atmosphere, to a stored carbon source.

This application is a continuation application of U.S. patentapplication Ser. No. 10/798,312 filed on Mar. 12, 2004 which is acontinuation-in-part of U.S. Pat. No. 6,736,955 filed on Nov. 2, 2001,which is allowed.

FIELD OF THE INVENTION

This invention relates to a method of methanol production having reducedemission of carbon dioxide.

BACKGROUND OF THE INVENTION

Methanol is a synthetic fuel which is produced from reactants whichprovide carbon, hydrogen and oxygen. There are various sources of eachof these molecules. For example, the requisite carbon may be obtainedfrom coal (see for example U.S. Pat. No. 4,476,249 Avery), natural gas(see for example U.S. Pat. No. 5,496,589 Fong et al.) and heavyhydrocarbons such as pitch and atmospheric and vacuum residues (see forexample Canadian Patent Application No. 2,060,108 Naber). Similarly, theoxygen and hydrogen, which are combined with the carbon during thesynthesis step to form methanol, may be obtained from various sources.These include electrolysis, as well as the water gas shift reaction. Forexample, Avery and U.S. Pat. No. 5,416,245 (McGregor et al.) disclosedthe use of electrolysis to provide hydrogen and oxygen. In the case ofAvery, the oxygen is added together with steam to a gasifier to producecarbon monoxide and hydrogen for synthesis (column 4, lines 46-50).

Methanol is advantageous as a substitute fuel for gasoline as well asdiesel fuel since it is a cleaner burning fuel (i.e. the fuel isconverted to carbon dioxide and water with fewer by-products beingproduced). The reduced emissions associated with methanol will not favorits production unless methanol can be produced in a cost effectivemanner. In the retail marketplace, methanol must be priced competitivelywith gasoline and diesel fuel to be a commercial alternative fuel.

The advantage of methanol being a low polluting fuel will be reduced, orpotentially lost, if the process for producing methanol has substantialemissions of greenhouse gases. Typical commercial processes, which arein operation to date, produce about 600 to 1200 pounds of carbon dioxideper ton of methanol produced. Therefore, while the methanol produced bythese processes may be relatively non-polluting compared to gasoline anddiesel fuel when it is combusted, when considered with the manufacturingprocess, the production and use of methanol may in fact be a substantialsource of greenhouse gases.

SUMMARY OF THE INVENTION

In accordance with the instant invention, a process for the productionof methanol is provided which has a reduced emission of carbon dioxideas a by-product of the manufacturing process. In particular, inaccordance with the instant invention, a process for the production ofmethanol may result in the emission of only 240 pounds of carbon dioxideper ton of methanol produced and, preferably, 120 pounds or less ofcarbon dioxide per ton of methanol produced. In one embodiment of thepresent invention, the process has a net consumption of CO₂. Forexample, the process may consume up to about 650 pounds of CO₂ per tonof methanol produced.

In accordance with one aspect of this invention, a partial oxidationreactor is utilized to produce the synthesis gas which is then subjectedto methanol synthesis to produce methanol and a tail gas stream. Thetail gas stream has unreacted synthesis gases (including carbon dioxide)therein. A purge stream is removed to prevent the build up of inertgases therein. The remainder of the stream, or essentially all of theremainder of the stream, is recycled to the partial oxidation reactor.In this way, carbon dioxide, as well as carbon monoxide and methane, maybe recycled through the system essentially to extinction except for thepurge stream. The amount of greenhouse gases emitted by the processeffectively depends upon the relative size of the purge gas stream tothe recycle stream. The larger of the recycle stream, the smaller thegreenhouse gases that are emitted. The recycle stream may comprise up to95 weight percent, and preferably from 50 to 95 weight percent of thetail gas stream, based on the weight of the tail gas stream.

In order to reduce the size of the purge stream, the introduction ofinert gases into the system is reduced. To this end, the oxygen which isused in the partial oxidation reactor preferably comprises essentiallypure oxygen. In prior art processes, air or oxygen enriched air isutilized. This results in the introduction of substantial quantities ofnitrogen. Not only does this result in the need to increase the size ofthe process equipment to have the same through put of methanol, but italso requires a larger purge stream and the consequential emission ofadditional greenhouse gases.

Typically, methanol production processes utilize reformers to provideadditional hydrogen to the synthesis gas to obtain the desiredstoichiometric ratio of hydrogen to CO and CO₂. Reformers, such as steamreformers, require the introduction of substantial quantities of waterinto the process and may result in the production of additional carbondioxide at the expense of carbon monoxide formation. However, in oneembodiment of the instant invention, a reformer is used to consumehydrogen in the conversion of CO₂ to CO. This is the reverse of thecurrent practice of operating a reformer. In accordance with anotheraspect of the instant invention, a hydrogen source other than reformersis utilized to adjust the hydrogen balance of the synthesis gas justahead of the methanol reactor. Preferably, at least some of the hydrogenis obtained by electrolysis and more preferably essentially all of thehydrogen is obtained by electrolysis.

In a further preferred aspect of the instant invention, at least some ofthe electricity which is utilized in operating the electrolysis step isobtained as off-peak or valley power from a power grid. Typically, thepower demand of a power grid varies throughout the day with the powerdemand from the grid being reduced at night when commercial andresidential requirements are reduced. Not only may off-peak or valleypower be obtainable at a reduced rate compared to peak demand time, but,in addition, the use of valley power may result in more efficientoperation of power generating plants. For example, if it is necessary toreduce the electrical output of a power generation plant, then theefficiency of the plant may be reduced. Alternately, it may not bepossible to reduce the power output of a generating plant thus resultingin the emission of greenhouse gases to produce power that is notrequired. Therefore, the use of valley power to run at least a portionof the electrolysis step may be highly beneficial. In fact, the oxygenand hydrogen produced by electrolysis such as at night may be stored instorage tanks so as to ensure a continuous supply of hydrogen andoxygen. Thus, if there is a power shortage during a peak demand period(e.g. during the day) then a continuous supply of hydrogen and oxygenmay be provided. In this way, the feed of raw materials to produce asynthesis gas may be leveled to ensure a uniform continuous supply. In afurther alternate embodiment, the electricity may be generated byrunning a fuel cell in reverse (i.e. a fuel cell may be operated toutilize an energy source such as electricity to produce hydrogen andoxygen).

Another advantage of the instant invention is that the amount ofhydrogen produced by the process may in fact exceed the amount ofhydrogen required to produce the desired stoichiometric balance of thesynthesis gas which is fed to the methanol synthesizer. Accordingly, theprocess may in fact also produce hydrogen as a valuable commercialproduct.

Accordingly, in accordance with this invention there is provided aprocess for the production of methanol comprising:

-   -   a) feeding an amount of a hydrocarbon feedstock and an amount of        an oxygen feedstock to a partial oxidation reactor to produce a        partial oxidation reactor effluent comprising hydrogen, carbon        monoxide and carbon dioxide;    -   (b) electrolyzing water to produce hydrogen and oxygen and        recovering at least a portion of the hydrogen to produce a        hydrogen stream;    -   (c) adding an amount of a hydrogen feedstock, at least a portion        of which is obtained from the hydrogen stream, to the partial        oxidation reactor effluent to produce a synthesis gas stream        having a predetermined ratio of hydrogen to carbon monoxide;    -   (d) subjecting the synthesis gas to methanol synthesis to        produce a methanol product stream and a tail gas stream;    -   (e) separating the tail gas stream into at least two streams        comprising a purge stream and a recycle stream, the recycle        stream comprising a substantial portion of the tail gas stream;        and,    -   (f) recycling the recycle stream to the partial oxidation        reactor.

In one embodiment, the process further comprises reforming the partialoxidation reactor effluent prior to the hydrogen addition step toconvert at least some of the carbon dioxide to carbon monoxide.Optionally, a carbon dioxide feed stream may be provided.

In another embodiment, the process further comprises the step ofrecovering at least a portion of the oxygen produced by electrolyzingwater to produce at least a portion of the oxygen feedstock.

In another embodiment, the process further comprises the step ofadjusting the amount of the oxygen feedstock to the amount of thehydrocarbon feedstock fed to the partial oxidation reactor such that thepartial oxidation reactor effluent contains some unoxidized hydrocarbonfeedstock. The partial oxidation reactor effluent may contain up toabout 10 wt % of the unoxidized hydrocarbon feedstock based on theweight of the partial oxidation reactor effluent and, preferably, thepartial oxidation reactor effluent contains less than about 4 wt % ofthe unoxidized hydrocarbon feedstock based on the weight of the partialoxidation reactor effluent.

In another embodiment, the process further comprises the step ofadjusting the amount of the oxygen feedstock to the amount of thehydrocarbon feedstock fed to the partial oxidation reactor such that thesynthesis gas, which is subjected to methanol synthesis, is essentiallyfree of oxygen.

In another embodiment, the synthesis gas which is subjected to methanolsynthesis has a ratio of hydrogen minus carbon dioxide mole fraction tocarbon dioxide plus carbon monoxide mole fraction of from about 1:1 toabout 3:1.

In another embodiment, the synthesis gas, which is subjected to methanolsynthesis has a ratio of hydrogen minus carbon dioxide mole fraction tocarbon dioxide plus carbon monoxide mole fraction is about 2:1.

In another embodiment, the tail gas stream contains nitrogen and themethod further comprises separating at least a portion of the nitrogenfrom the waste gas stream such that the purge stream is nitrogen richand the recycle stream is a nitrogen reduced waste gas stream.

In another embodiment, a membrane separator is used to separate the tailgas into the nitrogen reduced waste gas stream and the nitrogen richpurge stream.

In another embodiment, the process further comprises combusting thenitrogen rich purge stream to produce energy.

In another embodiment, the combustion of the purge stream produces heatthat is used to preheat at least one of the feedstocks of the partialoxidation reactor.

In another embodiment, the combustion of the purge stream produceselectricity that is preferably used to electrolyze water.

In another embodiment, the partial oxidation reactor produces waste heatand the waste heat is used to generate electricity.

In another embodiment, the electrolysis is conducted by running a fuelcell in reverse.

In another embodiment, essentially all of the hydrogen and the oxygen isobtained by electrolysis.

In another embodiment, at least a portion of electricity used toelectrolyze the water is valley power.

In accordance with another aspect of the instant invention, there isprovided a process for the production of methanol comprising:

-   -   (a) feeding an amount of a hydrocarbon feedstock and an amount        of an oxygen feedstock to a partial oxidation reactor to produce        a partial oxidation reactor effluent comprising hydrogen, carbon        monoxide and carbon dioxide;    -   (b) adding an amount of a hydrogen feedstock to the partial        oxidation reactor effluent to produce a synthesis gas stream        having a predetermined ratio of hydrogen to carbon monoxide;        and,    -   (c) subjecting the synthesis gas to methanol synthesis to        produce a methanol product stream and a tail gas stream wherein        reformation is not used to provide hydrogen as a product.

In one embodiment, the process further comprises the step of recycling aportion of the tail gas stream to the partial oxidation reactor.

In another embodiment, the process further comprising the step ofwithdrawing a purge stream from the tail gas stream and recyclingessentially the remainder of the tail gas stream to the partialoxidation reactor.

In accordance with another aspect of the instant invention, there isprovided a process for the production of methanol comprising:

-   -   (a) feeding a hydrocarbon feedstock to a partial oxidation        reactor to produce a synthesis gas comprising hydrogen, carbon        monoxide and carbon dioxide;    -   (b) subjecting the synthesis gas to methanol synthesis to        produce a methanol product stream and a tail gas stream;    -   (c) separating the tail gas stream into at least two streams        comprising a purge stream and a recycle stream, the recycle        stream comprising a substantial portion of the tail gas stream;        and,    -   (d) recycling the recycle stream to the partial oxidation        reactor.

In another embodiment, the tail gas stream contains nitrogen and step(c) comprises subjecting the tail gas stream to a separation processsuch that the recycle stream is nitrogen reduced and the purge stream isnitrogen rich.

In accordance with another aspect of the instant invention, a processfor the production of methanol comprising:

-   -   (a) electrolyzing water to produce hydrogen and oxygen and        recovering at least some of the hydrogen to produce a hydrogen        stream and recovering at least some of the oxygen to produce an        oxygen stream;    -   (b) feeding an amount of a hydrocarbon feedstock and an amount        of an oxygen feedstock, at least a portion of which is obtained        from the oxygen stream, to a partial oxidation reactor to        produce an effluent gas stream comprising hydrogen, carbon        monoxide and carbon dioxide;    -   (c) adding an amount of a hydrogen feedstock, at least a portion        of which is obtained from the hydrogen stream, to the partial        oxidation reactor effluent to produce a synthesis gas having a        predetermined ratio of hydrogen to carbon monoxide;    -   (d) subjecting the synthesis gas to methanol synthesis to        produce a methanol product stream and a tail gas stream:    -   (e) recycling a portion of the tail gas stream to the partial        oxidation reactor; and,    -   (f) combusting the purge stream to obtain energy wherein        reformation is not used to provide hydrogen as a product.

In one embodiment, the process further comprises combusting the nitrogenrich purge stream to produce energy.

In another embodiment, the combustion of the purge stream produces heatthat is used to preheat at least one of the feedstocks of the partialoxidation reactor.

In another embodiment, the combustion of the purge stream produceselectricity that is preferably used to electrolyze water.

In another embodiment, the partial oxidation reactor produces waste heatand the waste heat is used to generate electricity.

In another embodiment, the electrolysis is conducted by running a fuelcell in reverse.

In accordance with another embodiment of the instant invention, aprocess for the production of methanol comprises:

-   -   (a) feeding an amount of a hydrocarbon feedstock and an amount        of an oxygen feedstock to a partial oxidation reactor to produce        a partial oxidation reactor effluent comprising hydrogen, carbon        monoxide and carbon dioxide;    -   (b) electrolyzing water to produce hydrogen and oxygen and        recovering at least a portion of the hydrogen to produce a        hydrogen stream;    -   (c) reacting carbon dioxide with hydrogen to produce carbon        monoxide; and,    -   (d) subjecting a methanol synthesis gas obtained from the        partial oxidation reactor effluent, at least a portion of the        hydrogen stream and carbon monoxide produced by step (c) to        methanol synthesis to produce a methanol product stream and a        tail gas stream.

In one embodiment, the process as further comprises separating the tailgas stream into at least two streams comprising a purge stream and arecycle stream, the recycle stream comprising a substantial portion ofthe tail gas stream; and recycling the recycle stream to the partialoxidation reactor.

In another embodiment, the partial oxidation reactor effluent is fed toa reformer to produce a reformed synthesis gas and at least a portion ofthe hydrogen stream is combined with the reformed synthesis gas toproduce the methanol synthesis gas.

In another embodiment, the process further comprises combining a carbondioxide feedstock with the partial oxidation reactor effluent to producea carbon dioxide rich synthesis gas stream and feeding the carbondioxide rich synthesis gas stream to the reformer to produce a reformedsynthesis gas.

In another embodiment, at least a portion of the hydrogen stream iscombined with the reformed synthesis gas to produce the methanolsynthesis gas.

In another embodiment, wherein at least a portion of the hydrogen streamis introduced to the reformer or a feedstream to the reformer.

In accordance with any aspect of this invention, the hydrocarbonfeedstock may include carbon dioxide. In such a case, additional carbondioxide may provided by a carbon dioxide feed stream and at least aportion of the carbon dioxide stream is obtained from biogas.Alternately, the additional carbon dioxide may be provided by a carbondioxide feed stream obtained from any standard source in the industry.

In accordance with any aspect of this invention the hydrocarbonfeedstock is obtained from biogas and includes carbon dioxide. Thecarbon dioxide feed stream may be provided upstream from the partialoxidation reactor. Alternately, or in addition, the carbon dioxide feedstream is provided downstream from the partial oxidation reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the instant invention may be morecompletely fully understood by means of the following description of theaccompanying drawings of the preferred embodiments of the instantinvention in which:

FIG. 1 is a schematic drawing of a preferred embodiment of the instantinvention;

FIG. 2 is a schematic drawing of an alternate preferred embodiment inaccordance with the instant invention;

FIG. 3 is a schematic drawing of a further alternate preferredembodiment in accordance with the instant invention; and,

FIG. 4 is a schematic drawing of a further alternate preferredembodiment in accordance with the instant invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, according to a preferred embodiment of the instantinvention, the process comprises partial oxidation reactor 10 andmethanol synthesis reactor 12. Hydrocarbon feedstock 14 and oxygenfeedstock 16 are fed to partial oxidation reactor 10 to producesynthesis gas 18. Hydrogen feedstock 20 is combined with synthesis gas18 to produce synthesis gas 22 wherein the stoichiometric balance hasbeen adjusted. The adjusted synthesis gas 22 is fed to methanolsynthesis reactor 12 to produce tail gas 24 and methanol 26.

In steam reformation processes, steam is added to a reformer. Further,the hydrocarbon feedstock fed to the stream reformer may be humidified(which provides a further source of water). Overall, the process gasstreams contain substantial quantities of water and the methanolproduced typically is treated such as by distillation to reduce thewater content of the methanol. In accordance with one embodiment of theinstant process a hydrogen gas stream which is relatively pure (e.g.more than about 97 weight percent hydrogen and more preferably more thanabout 99 weight percent hydrogen) is preferably utilized to adjust thechemical balance of the synthesis gas. In accordance with thisembodiment, water need not be added to the process and is preferably notadded to the process (except in so far as some quantities may becontained with the hydrocarbon feedstock such as may be contained forexample in natural gas). Accordingly, the amount of water travelingthrough the process and accordingly exiting methanol synthesis reactor12 is substantially reduced compared to steam reformation processes.Accordingly, methanol 26 may have a relatively low level of water.

Methanol which contains as much as 10 weight percent water may be burnedin convention combustion devices such as an internal combustion engine.In accordance with this embodiment of the instant invention, by avoidingthe use of reformation in the process, methanol 26 (which is the productproduced directly from methanol synthesis reactor 12 withoutdistillation) may contain less than this amount of water andaccordingly, may be a commercial product without further processing.More preferably, methanol stream 26 contains less than 6 weight percentwater and, more preferably, less than about 2 weight percent water.

Hydrocarbon feedstock 14 may be any gaseous or liquid hydrocarbon, ispreferably a gaseous hydrocarbon and, more preferably comprises asubstantial quantity of methane (e.g. more than 90 weight percent). Inone particular embodiment, hydrocarbon feedstock 14 preferably comprisesand, more preferably, consists essentially of natural gas or methane. Inan alternate preferred embodiment, some or all of the hydrocarbonfeedstock may be obtained from biomass. Biomass may comprise one or moreof manure, silage, agricultural waste, peat and organic household waste.Many sources of biomass are known to those skilled in the waste disposalart. The anaerobic decomposition of biomass produces biogas whichcomprises one or more of methane, carbon dioxide, hydrogen, hydrogensulfide, nitrogen and other components. The actual composition of thebiogas will vary depending upon the biomass which is used as a feedstockand if any oxygen is present (in which case some aerobic decompositionwill occur). If biogas is used as a feedstock, then some pollutants suchas hydrogen sulfide are preferably removed by any separation techniqueknown in the art prior to the biogas being used as a feedstock for themethanol production process described herein. Alternately, or inaddition, the biogas may be treated to obtain a methane stream. Thebiogas, or a methane stream obtained from the biogas, may be used as asource of some or all of the hydrocarbon required for the methanolproduction process and may be fed to the process in any manner disclosedherein. For example such a methane stream and/or the biogas may formpart or all of hydrocarbon feedstock 14.

As shown in FIG. 2, oxygen feedstock 16 may be obtained by electrolysis.In particular, water 32 is feed to electrolysis unit 28 to produceoxygen stream 16 and hydrogen stream 34. Some or all of oxygen stream 16may be fed directly to partial oxidation reactor 10 as oxygen stream 16′(as shown by the broken feed line shown in FIG. 2). Similarly, some orall of hydrogen stream 34 may be fed directly to synthesis gas 18 ashydrogen stream 20 (as shown by the broken feed line shown in FIG. 2).Preferably, storage tanks are utilized to produce a generally continuousflow of hydrogen and oxygen to streams 16′ and 20. To this end, one ormore oxygen storage tanks 36 and one or more hydrogen storage tanks 38may be provided.

In operation, electricity for electrolysis unit 28 may be obtained froma power grid. During peak periods, when the cost of electricity isgreater or, in some cases, when the requisite amount of electricity maynot be available, the production of hydrogen and oxygen by electrolysisunit 28 may be reduced. In such cases, the amount of hydrogen and oxygendelivered to storage tanks 36 and 38 is reduced. However, depending uponthe capacity of storage tanks 36 and 38, the process may be suppliedwith hydrogen and oxygen via streams 42 and 40 at about the same rateregardless of the flow rate of hydrogen and oxygen into tanks 36 and 38via streams 32 and 34. In this way, tanks 36 and 38 may be utilized toproduce a continuous flow of hydrogen and oxygen to the process.

In another embodiment of the instant invention, electrolysis unit 28 mayproduce excess hydrogen and oxygen then are required for the operationof partial oxidation and methanol synthesis reactors 10 and 12. In suchcases, the excess amounts may be withdrawn as product oxygen stream 44and/or product hydrogen stream 46. Alternately, or in addition, some orall of the hydrogen may be obtained from biogas. For example, a biogasmay be treated to obtain a hydrogen stream which may be used, e.g., asall or part of hydrogen feedstock stream 20. Alternately, or inaddition, if a biogas is used to provide some or all of the hydrocarbonrequirement, then hydrogen may be provided with the biogas whichsupplies the hydrocarbon requirement. For example, if biogas is used toprovide part or all of hydrocarbon feedstock stream 14, then the biogasmay be treated to remove pollutants leaving a stream containing methaneand hydrogen. Alternately, the biogas may be treated to produce a streamcontaining methane and hydrogen.

In one embodiment, synthesis gas 22 has a ratio of hydrogen minus carbondioxide mole fraction to carbon dioxide plus carbon monoxide molefraction of from about 1.1 to about 3.1 and, preferably, the ratio isabout 2.1. To achieve these ratios, particularly if hydrocarbonfeedstock 14 substantially comprises or consists essentially of methane,a greater proportion of the oxygen produced by electrolysis unit 28 willbe required then the hydrogen produced by electrolysis unit 28.Accordingly, then in one embodiment of operation, electrolysis unit 28may be operated to produce essentially the requisite amount of oxygen toproduce this ratio resulting in essentially no product oxygen stream 44.However, as less hydrogen will be required to produce the desired ratio,only a portion of the hydrogen produced by electrolysis unit 28 need becombined with synthesis gas 18 via stream 20. Accordingly, the overallprocess will be a net producer of not only methanol but also hydrogen aswell via stream 46.

In accordance with another aspect of the instant invention, the processis preferably operated such that synthesis gas 22 essentially containsno oxygen (e.g. less than about 0.5 weight percent). If the oxygencontent of the synthesis gas is too high, then oxygen will react withmethanol in methanol synthesis reactor 12 to form carbon dioxide andwater. To reduce the amount of oxygen in the synthesis gas, the amountof hydrocarbon feedstock 14 fed to partial oxidation reactor 10 ispreferably adjusted, based upon the flow rate of oxygen stream 16 topartial oxidation reactor 10 such that the effluent from partialoxidation reactor 10 contains at least some unoxidized hydrocarbonfeedstock. Preferably, the effluent contains from less than about 10weight percent of the unoxidized hydrocarbon feedstock and, morepreferably, less than about 4 weight percent of the unoxidizedhydrocarbon feedstock, based on the weight of the effluent stream. Atthese levels, essentially all of the oxygen will be utilized in partialoxidation reactor 10. It will be appreciated by those skilled in the artthat the actual amount of unoxidized hydrocarbon which is required willvary in part depending upon the efficiency of partial oxidation reactor10.

Referring to FIG. 3, in a further embodiment of the instant invention,tail gas stream 24 is subjected to gas separation unit 48 to producetail gas recycle stream 50 and purge stream 52. Preferably, gasseparation unit 48 utilizes cryogenic separation or a membrane separatorand, more preferably, a membrane separator. Purge stream 52 is utilizedto remove inert material such as nitrogen, argon and the like. The inertmaterial that is to be removed will vary depending upon the contaminantsin the feedstocks. For example, if hydrocarbon feedstock stream 14 isnatural gas, purge stream 52 is utilized to remove, for example,nitrogen that is present with the natural gas. The substantial portionof the tail gas is recycled as recycle stream 50. In particular, recyclestream 50 may comprise up to about 95 weight percent and, morepreferably from about 50 to about 95 weight percent of tail gas stream24. Accordingly, a substantial portion of an unreacted synthesis gas isrecycled into the system. As shown in FIG. 3, recycle stream 50 ispreferably combined with hydrocarbon feedstock stream 14 to produceblended hydrocarbon stream 54 which is then fed to partial oxidationreactor 10. Alternately, recycle stream 50 may be fed directly topartial oxidation reactor 10. In either case, the unreacted synthesisgases, which include carbon dioxide, is recycled through the partialoxidation reactor wherein some of the carbon dioxide may be converted tocarbon monoxide which is then combined with hydrogen in the methanolsynthesis reactor 12 to produce methanol. The conversion of the carbondioxide to carbon monoxide may occur in an optional reformer 46.However, at the high temperatures of the gasses, this reaction may alsooccur to an extent in the fluid conduits in which the gasses are at asufficiently high temperature (e.g. synthesis gas effluent 18 frompartial oxidation reactor 10) and in heat exchangers.

Purge stream 52 may be fed to a combustion unit 56, such as a gasturbine, to produce power 58 and stack gases 60. Power 58 may be in theform of mechanical power or electricity if combustion unit 56 isdrivingly connected to a generator.

Stack gases will be at an elevated temperature. Accordingly, excess heatfrom stack gases 60 may be recovered by means of heat exchanger 62. Forexample, water 64 may be fed to heat exchanger 62 to indirectly heat thewater to produce steam 66 and cooled stack gases 68. In an alternateembodiment, shown in FIG. 1, purge gas 52 may be utilized to preheat afeedstock, e.g. hydrocarbon feedstock 14. In such a case, purge stream52 may be fed directly to indirect exchanger 62 or it may first be fedto combustion unit 56 to further increase the temperature of the purgestream prior to the heat exchange step.

In a further alternate embodiment shown in FIG. 2, the excess heatgenerated by partial oxidation reactor 10 may be recovered to producesteam and, more preferably electricity. For example, referring to FIG.2, partial oxidation reactor 10 may be provided with a jacket (e.g. acooling jacket fed with water 72). The water is heated and thusmoderates the temperature of partial oxidation reactor 10. The water maybe heated by its passage through jacket 70 to such an extent that itproduces stream 74 which may be steam. Alternately, stream 74 may besuperheated water which, upon passage though turbine 76 produceselectricity 78 and water or wet steam 80.

In accordance with another embodiment of the instant invention, carbondioxide in synthesis gas 18 and/or carbon dioxide from a feedstock 82 isconverted to carbon monoxide to provide additional feed gas forconversion to methanol (see FIG. 4). Pursuant to this embodiment,reformer 86 is provided downstream from partial oxidation reactor 10.Synthesis gas 18 is fed to reformer 86. Conventionally, a reformer isoperated to provide hydrogen as a product. In accordance with thisembodiment, reformer 86 is operated to convert carbon dioxide to carbonmonoxide by the overall reaction:

CO₂+H₂→ CO+H₂O

Accordingly, hydrogen from one of the feedstocks is consumed by theprocess. As discussed previously, the instant process may be conductedto produce product hydrogen stream 46. According to this embodiment, atleast a portion of the product hydrogen stream could effectively be usedby reformer 86. In this way, the amount of product hydrogen stream 46may be reduced or eliminated depending on the amount of hydrogenrequired for reformer 86. By operating a reformer effectively inreverse, the product of the reformer (reformed synthesis gas stream 84)will contain water. Typically, reformer 86 will be operated at apressure less than methanol synthesis reactor 12 and at a highertemperature. As the temperature of reformed synthesis gas stream 84 isreduced and the pressure is increased so that reformed synthesis gasstream 84 is suitable for feeding to methanol synthesis reactor 12,water may be removed from reformed synthesis gas stream 84. In this way,water production is shifted away from methanol synthesis reactor 12 andthe purity of the product methanol stream 26 is increased.

The carbon dioxide for reformer 86 may be supplied from synthesis stream18. Alternately, or in addition, a carbon dioxide feedstock stream 82may be provided. Carbon dioxide feedstock stream 82 may be obtained fromvarious sources and is preferably relatively pure since any contaminantswill have to be purged from the system or will contaminate the methanolproduced by the process. Carbon dioxide feedstock stream 82 may beobtained as excess carbon dioxide from a bottling plant or as exhaustgas produced by combustion. In the later case, the exhaust gas ispreferably subjected to cleaning steps to remove undesirablecontaminants. The carbon dioxide is preferably obtained as a by productof another process so that the instant process becomes effectively atemporary carbon sink to convert carbon dioxide, which would otherwisebe released to the atmosphere, to a stored carbon source. For example,some or all of the carbon dioxide may be obtained from biogas. In oneembodiment, a biogas may be treated to obtain a carbon dioxide streamwhich may be used, e.g., as all or part of carbon dioxide stream 82.Alternately, or in addition, if biogas is used to provide part or all ofhydrocarbon feedstock stream 14, then the biogas may be treated toremove pollutants leaving a stream containing methane and carbondioxide. Alternately, the biogas may be treated to produce a streamcontaining methane and carbon dioxide.

Reformed synthesis gas stream 84 may be treated as discussed previously.Alternately, hydrogen may be added to the process upstream of reformer86 (as shown by the dashed line in FIG. 4) or directly to reformer 84(as shown by the dashed line in FIG. 4).

It will be appreciated by those skilled in the art that each of theembodiments of the instant invention may be utilized individually orcombined to produce an improved process for the production of methanol.

1. A process for the production of methanol comprising: (a) feeding anamount of a hydrocarbon feedstock and an amount of an oxygen feedstockto a partial oxidation reactor to produce a partial oxidation reactoreffluent comprising hydrogen, carbon monoxide and carbon dioxide; (b)adding an amount of a hydrogen feedstock that is exogenous to thehydrocarbon feedstock to the partial oxidation reactor effluent toproduce a synthesis gas stream having a predetermined ratio of hydrogento carbon monoxide; and, (c) subjecting the synthesis gas stream tomethanol synthesis to produce a methanol product stream and a tail gasstream wherein reformation is not used to provide the hydrogenfeedstock.
 2. The process as claimed in claim 1 further comprisingelectrolyzing water to produce hydrogen and oxygen and recovering atleast some of the hydrogen to produce at least a portion of the hydrogenfeedstock.
 3. The process as claimed in claim 2 further comprising thestep of recovering at least a portion of the oxygen from the waterelectrolysis to produce at least a portion of the oxygen feedstock. 4.The process as claimed in claim 1 further comprising the step ofadjusting the amount of the oxygen feedstock to the amount of thehydrocarbon feedstock fed to the partial oxidation reactor such that thepartial oxidation reactor effluent contains some unoxidized hydrocarbonfeedstock.
 5. The process as claimed in claim 4 wherein the partialoxidation reactor effluent contains less than about 10 wt % unoxidizedhydrocarbon feedstock based on the weight of the partial oxidationreactor effluent.
 6. The process as claimed in claim 4 wherein thesynthesis gas contains less than about 4 wt % unoxidized hydrocarbonfeedstock based on the weight of the partial oxidation reactor effluent.7. The process as claimed in claim 1 further comprising the step ofadjusting the amount of the oxygen feedstock to the amount of thehydrocarbon feedstock fed to the partial oxidation reactor such that thepartial oxidation reactor effluent is essentially free of oxygen.
 8. Theprocess as claimed in claim 1 wherein the synthesis gas which issubjected to methanol synthesis has a ratio of hydrogen minus carbondioxide mole fraction to carbon dioxide plus carbon monoxide molefraction of from about 1:1 to about 3:1.
 9. The process as claimed inclaim 1 wherein the synthesis gas, which is subjected to methanolsynthesis, has a ratio of hydrogen minus carbon dioxide mole fraction tocarbon dioxide plus carbon monoxide mole fraction which is about 2:1.10. The process as claimed in claim 1 further comprising the step ofrecycling a portion of the tail gas stream to the partial oxidationreactor.
 11. The process as claimed in claim 1 further comprising thestep of withdrawing a purge stream from the tail gas stream andrecycling essentially the remainder of the tail gas stream to thepartial oxidation reactor.
 12. The process as claimed in claim 1 whereinthe tail gas stream contains nitrogen and the process further comprisesseparating at least a portion of the nitrogen from the waste gas streamto produce a nitrogen rich purge stream and a nitrogen reduced waste gasstream that is recycled to the partial oxidation reactor.
 13. Theprocess as claimed in claim 12 wherein a membrane separator is used toseparate the tail gas stream into the nitrogen reduced waste gas streamand the nitrogen rich purge stream.
 14. The process as claimed in claim12 further comprising combusting the nitrogen rich purge stream toproduce energy.
 15. The process as claimed in claim 14 wherein thecombustion of the purge stream produces heat that is used to preheat atleast one of the feedstocks of the partial oxidation reactor.
 16. Theprocess as claimed in claim 14 further comprising electrolyzing water toproduce hydrogen and oxygen and recovering at least some of the hydrogento produce at least a portion of the hydrogen feedstock and wherein thecombustion of the purge stream produces electricity.
 17. The process asclaimed in claim 12 wherein the partial oxidation reactor produces wasteheat and the waste heat is used to generate electricity.
 18. The processas claimed in claim 2 wherein the electrolysis is conducted by running afuel cell in reverse.
 19. The process as claimed in claim 1 wherein atleast a portion of at least one of the hydrocarbon feedstock and thehydrogen feedstock is obtained from biogas.
 20. The process as claimedin claim 1 wherein the hydrocarbon feedstock includes carbon dioxide.21. The process as claimed in claim 20 wherein additional carbon dioxideis provided by a carbon dioxide feed stream and at least a portion ofthe carbon dioxide stream is obtained from biogas.
 22. The process asclaimed in claim 20 wherein additional carbon dioxide is provided by acarbon dioxide feed stream.
 23. The process as claimed in claim 1wherein the hydrocarbon feedstock is obtained from biogas and includescarbon dioxide.
 24. The process as claimed in claim 21 wherein thecarbon dioxide feed stream is provided upstream from the partialoxidation reactor.
 25. The process as claimed in claim 21 wherein thecarbon dioxide feed stream is provided downstream from the partialoxidation reactor.
 26. The process as claimed in claim 19 wherein thebiogas is obtained from anaerobic decomposition of biomatter. 27-52.(canceled)